This invention relates to spherical, expandable hollow bodies of solidified alkali metal silicate solutions, to processes for their production and to their use.
In the context of the invention, solidified alkali metal silicate solutions are understood to be the products formed by the reaction of alkali metal silicate solutions with so-called hardeners. Known hardeners are, in particular, carboxylic acids and their derivatives, such as the corresponding esters, acid chlorides and amides. Other known hardeners include ammonium salts and salts of polyvalent metals, mineral acids and acid salts thereof and also hexafluorosilicates.
The hardening process can be controlled through the choice of the hardener. Slow reactions are obtained above all with the carboxylic acid derivatives and with hexafluorosilicates. Rapid solidification is obtained when mineral acids and salts of polyvalent metals are used.
These processes have been repeatedly described in the literature and have also been used for producing foam bodies of waterglass or porous granulate-containing bodies which, by virtue of their low density, are of interest as fillers and insulating materials.